How Do You Diagnose and Manage Migraine Aura?
The patient has what sounds like the visual aura of migraine. She sees a jagged line in her peripheral vision that gets bigger over about 5 minutes and then moves across her visual field. However, she denies headache and has no previous history of migraine headaches. Can this still be migraine?
Aura is defined as a sensory warning that usually announces the onset of a more explicit neurological event, like a migraine headache or a major motor seizure. Visual auras in migraine may manifest as a transient negative scotoma (eg, homonymous hemianopia), monocular visual loss, or as a positive scotoma (eg, a luminous, colorful display of sparkling, dazzling, dancing, or flickering lights arrayed geometrically in homonymous portions of the visual field). While most migrainous auras herald the onset of a headache, 13% of migraineurs have the visual symptoms without headache, in which case the isolated visual experience is nosologically referred to as migraine aura without headache (acephalgic migraine).
An isolated, transient homonymous hemianopia, visual illusion, or visual hallucination can be caused by other conditions besides migraine. Thus, it behooves you to know the characteristic features of a migrainous aura and to know when and how aggressively to pursue other etiologies, when sufficient doubt exists.
The prototypic migraine aura begins as a small flickering ill-defined spot eccentric to fixation. The patient may be aware of something obscuring vision but often has difficulty describing it. Over 15 to 30 minutes, the obscuration enlarges and marches across the homonymous portions of visual field, leaving behind a wake of blindness that slowly fills in as the scintillation fades into the temporal periphery of the ipsilateral eye. If your patient claims that his or her experience was monocular, ask him or her to cover each eye independently at the onset of the next attack because he or she will often see a nasal defect or display in the less involved eye, thus establishing the symptoms as homonymous and more likely due to migraine.
Additional subtleties of the history that help to confirm the diagnosis of migraine aura without headache include the following: if the aura was preceded by or followed by another type of migraine accompaniment, such as paresthesias (pins and needles) that marched up one extremity and crossed to the other side; if certain situations predictably provoke visual symptoms or headache, like sleeplessness, hunger, alcohol consumption, or menses; a history of previous migraine headaches, with or without aura, as the syndrome of migraine aura without headache often occurs in patients who have had other types of migraine; and whether 2 or more identical episodes have occurred, especially months or years apart, with full recovery each time.
In contrast to the characteristic features of a migraine aura, the following atypical historical points or physical findings should alert you to the possibility of an alternative etiology: visual symptoms exclusively confined to the same side of the visual field; visual aura accompanied by a change in consciousness or followed by a persistent visual deficit, hemiparesis, hemisensory loss, or incontinence; monocular or bitemporal visual symptoms; or a recent flurry of transient symptoms with different neuro-ophthalmological manifestations (eg, an homonymous hemianopia one time and a transient hemiparesis or hemisensory loss another time).
Virtually all patients with transient visual phenomena see a physician after their vision has returned to normal. Accurate diagnosis, therefore, is predicated on meticulous history taking and the following observations during your physical examination: auscultation of the orbits, cranial vault, and neck vessels to listen for a bruit; direct and indirect ophthalmoscopy of both eyes to look for intravascular plugs or plaques, isolated or multiple retinal infarctions, or signs of venous stasis retinopathy; and quantitative visual field testing to detect an asymptomatic defect that topographically localizes to the retrochiasmal visual pathways.
An atypical history or the foregoing physical findings warrant a thorough evaluation of the following conditions: focal epilepsy, recurrent microemboli, structural lesions of the occipital lobe (arteriovenous malformation or brain tumor), hematological disorders, and collagen vascular disease. I also have a lower threshold for pursuing the differential diagnosis in the elderly because they often cannot recount the small, but characteristic details of their visual experience, and thromboembolism is more prevalent in their age group. That said, if the description of a transient visual event is sufficiently characteristic of migraine (build-up, march, and duration), I have yet to find an alternative etiology, which has over years of experience led me to the conclusion that very few nonmigrainous conditions mimic a characteristic migraine aura without headache.
Differentiating migraine from focal epilepsy may sometimes be difficult, particularly in children, since each condition may cause paroxysmal symptoms that march over time. Frequently, however, occipital epileptogenic discharges also produce tonic deviation of the eyes, vomiting, and a unilateral or generalized convulsion. Thromboembolism may indeed cause a transient homonymous hemianopia and should be considered in the elderly or in persons with evidence of arteriosclerotic risk factors (smoking, obesity, diabetes, hypertension, dyslipidemia, family predilection for premature vascular disease) or cardiac conditions that may cause thromboembolism (eg, valvular damage, recent myocardial infarction, cardiomyopathy). I was taught the clinical adage that vertebrobasilar artery disease commonly causes transient homonymous hemianopia and blindness, yet it occurs as the isolated manifestation in less than 2% of cases.
Although build-up, march, and duration help to distinguish a migraine aura, 25% of migraineurs state that their visual loss or display becomes maximum immediately. The absence of build-up should not exclude migraine but should at least engender a consideration of the differential diagnosis. In a thromboembolic transient ischemic attack (TIA), the sensory loss on the face, arm, and leg occur simultaneously, while the march of sensory symptoms in migraine gradually spreads over the face, fingers, or hand and migrates and crosses to the contralateral face and hand over 30 minutes. In general, the duration of a migrainous aura lasts 15 to 25 minutes, whereas 95% of TIAs last less than 15 minutes.
In my opinion, the indications for doing a magnetic resonance imaging (MRI) scan of the brain with and without contrast administration and/or MR angiography (MRA) of the intracranial or extracranial vessels in persons with migraine aura without headache or other headache syndromes include the following: atypical history or physical findings, rapidly increasing frequency and/or severity of auras alone or headaches, first or “worst” headache ever experienced, thunderclap or abrupt-onset incapacitating headache, new onset of headache or migraine aura without headache after age 50, and a headache or headaches that are refractory to traditional treatment.
Differential diagnosis of transient physical phenomena in the presence of normal imaging studies includes thrombocythemia, thrombotic thrombocytopenia, polycythemia, and other hyperviscosity states or clotting disorders.
Once confident that you are dealing with the diagnosis of migraine aura without headache, the treatments of choice are reassurance, reassurance, and more reassurance. Sometimes telling the patient to rebreathe their own air abbreviates or aborts the visual symptoms because increased blood carbon dioxide levels cause cerebral vasodilation, and theoretically should reverse the visual pathway dysfunction possibly caused by migrainous cerebral vasoconstriction. If visual symptoms become so frequent as to interfere with the quality of life of the patient, referral to a neurologist for further treatment is warranted.
* Migraine aura is a clinical diagnosis.
* Once confident that you are dealing with the correct diagnosis of migraine aura without headache, the treatment of choice is reassurance, reassurance, and more reassurance.
* If visual symptoms become so frequent as to interfere with the quality of life of the patient, referral to a neurologist should be considered.
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